Kinetic Study on the Reduction of Room-Temperature NO_x in Etching Waste Gas by Na₂S₂O₅ and Urea in Alkaline Pretreatment

Abstract

Etching waste gases derived from photovoltaic cell production are difficult to treat at room temperature. Therefore, the use of wet denitrification with Na 2 S 2 O 5 is recommended to overcome this issue. The presence of O 2 , Cl 2 , and metals in gases leads to the consumption of 65% of SO 3 2− within 2 h. Although alkaline pretreatment adsorbs most of the gases and metals, the high ceiling temperature results in a short residence time and incomplete reaction with the lye. Therefore, in this study, urea was added to Na 2 S 2 O 5 . After adding the optimum concentration of urea (0.5 mol L −1 ) to a 1.0 mol L −1 SO 3 2− solution, the anodic potential measured using cyclic voltammetry shifted from 0.051 to −0.119 V, the electron transfer rate k 0 decreased from 4.89 × 10 −5 to 4.27 × 10 −5 cm s −1 , the exchange current density measured using the polarization curve decreased from 18.37 to 13.58 A cm −2 , and the reaction activation energy increased from 37 to 63 kJ mol −1 . Therefore, adding urea to generate hydroxyl functional groups can effectively block the free radical oxidation chain reaction of SO 3 2− , hindering its oxidization. In summary, alkaline pretreatment and urea addition can increase the effective reaction between SO 3 2− and NO x and reduce the costs. Our study provides data to support the application of wet denitrification at room temperature.